Fine Bubble Generating Apparatus

ABSTRACT

This invention provides a fine bubble generating apparatus which can efficiently generate fine bubbles on the nanometer level. This apparatus comprises a cylindrical member ( 40 ) having a cylindrical inner peripheral surface, a first end wall member ( 42 ) configured to close one end of the cylindrical member, and a second end wall member ( 44 ) configured to close the other end of the cylindrical member. The cylindrical member ( 40 ) and the first and second end wall members ( 42 ) and ( 44 ) define a fluid swirling chamber ( 46 ). The cylindrical member has a fluid inlet hole ( 48 ) at a position close to the second end wall member ( 44 ) to supply a gas-liquid mixed fluid in the tangential direction of the peripheral surface of the fluid swirling chamber ( 46 ). The second end wall member has a fluid outlet hole ( 50 ) extending therethrough along the center axis of the inner peripheral surface of the fluid swirling chamber. The gas-liquid mixed fluid is introduced into the fluid swirling chamber at a position close to the second end wall member. Most of the fluid is directed toward the first end wall member while swirling along the inner peripheral surface of the fluid swirling chamber, reversed from the first end wall member toward the second end wall member and discharged through the fluid outlet hole.

TECHNICAL FIELD

The present invention relates to apparatus for generating fine bubblesand, more particularly, to a fine bubble generating apparatus that cangenerate a large amount of nanobubbles having a diameter of nanometerlevel.

BACKGROUND ART

Recently, attention has been paid to various methods of utilizing finebubbles having a diameter of micrometer level or nanometer level, andvarious apparatus for generating fine bubbles have been proposed. Thepresent invention relates to an apparatus having a cylindrical interiorspace, wherein a gas-containing liquid is introduced into the interiorspace to generate a swirling flow to break up the gas into fine bubblesby the shear force of the swirling flow.

An apparatus of the type described above is disclosed, for example, inJapanese Patent Application Publication No. 2001-276589. The apparatusdisclosed in this publication has a cylindrical swirling flow generatingmember immersed vertically in a liquid in a liquid storage tank forgenerating fine bubbles. The swirling flow generating member has oneinlet hole provided in an upper end portion thereof to introduce agas-liquid mixed fluid. The inlet hole tangentially intersects the innerperipheral surface of the cylindrical member. A funnel-shaped portion isprovided at the lower end of the swirling flow generating member. Thefunnel-shaped portion has a fluid outlet at the lower end thereof. Apipe is connected to the inlet hole to supply a pressurized fluid from apump. An aspirator is connected to an intermediate portion of the pipe.A liquid mixed with air as bubbles is passed through the aspirator andintroduced into the swirling flow generating member through the inlethole. The introduced gas-liquid mixed fluid moves downward whileswirling in the swirling flow generating member and is discharged intothe liquid storage tank through the fluid outlet at the lower end of theswirling flow generating member. A shear force occurs between thedischarged gas-liquid mixed fluid and the liquid in the storage tank.Thus, the bubbles in the gas-liquid mixed fluid are broken up into finebubbles.

Japanese Patent Application Publication No. 2003-117368 discloses a finebubble generating apparatus including a cylindrical member having aninner peripheral surface formed into a cylindrical shape or the like. Inthis apparatus, a liquid, together with air, is introduced into a pumpfor liquid supply to form a gas-liquid mixed fluid containing bubbles inthe pump, and the gas-liquid mixed fluid is introduced into thecylindrical member through one inlet hole provided in the cylindricalmember close to one end thereof. The introduced gas-liquid mixed fluidmoves axially toward the other end of the cylindrical member whileswirling and is discharged through an outlet provided at the other endof the cylindrical member. Thus, the bubbles in the gas-liquid mixedfluid are broken up into fine bubbles. This publication also disclosesan apparatus wherein a gas-liquid mixed fluid is introduced into acylindrical member through an inlet hole provided in an axially centralportion thereof, and the introduced gas-liquid mixed fluid moves towardboth ends of the cylindrical member while swirling and is dischargedthrough outlets provided at both ends of the cylindrical member.

Japanese Patent No. 3682286 discloses a bubble breaking-up apparatusincluding a swirling flow generating member with an oval or ellipticalinner peripheral surface that is immersed in a liquid in a liquidstorage tank. In this apparatus, the swirling flow generating member hasone inlet hole for introducing a gas-liquid mixed fluid at the center ofthe major axis of ellipse. The gas-liquid mixed fluid introduced throughthe inlet hole moves in a swirling flow toward outlets provided at bothends in the major axis direction of the swirling flow generating memberand is discharged through the outlets. It is stated that the gas in thegas-liquid mixed fluid is broken up into fine bubbles by swirling flowin the swirling flow generating member and shear force applied to thegas-liquid mixed fluid when discharged.

Japanese Patent Application Publication Nos. 2002-11335 and 2002-166151disclose an apparatus wherein a gas-liquid mixed fluid is introducedinto a swirling flow generating member having a cylindrical innerperipheral surface through two axially spaced gas-liquid mixture inletholes provided in the swirling flow generating member, and theintroduced gas-liquid mixed fluid is discharged through outlets providedat both ends of the swirling flow generating member.

Patent Document 1: Japanese Patent Application Publication No.2001-276589 Patent Document 2: Japanese Patent Application PublicationNo. 2003-117368 Patent Document 3: Japanese Patent No. 3682286 PatentDocument 4: Japanese Patent Application Publication No. 2002-11335Patent Document 5: Japanese Patent Application Publication No.2002-166151 DISCLOSURE OF THE INVENTION Problem to be Solved by theInvention

All the above-described fine bubble generating apparatus break upbubbles contained in a gas-liquid mixed fluid into fine bubbles bygenerating a swirling flow in the fluid. None of them, however, canefficiently generate nanometer-level bubbles (nanobubbles).

An object of the present invention is to provide a fine bubblegenerating apparatus that can efficiently generate nanobubbles.

Means for Solving the Problem

The present invention provides a fine bubble generating apparatusincluding a gas swirling shearing unit. The gas swirling shearing unitincludes a cylindrical member having a cylindrical inner peripheralsurface, a first end wall member configured to close one end of thecylindrical member, a second end wall member configured to close theother end of the cylindrical member, a fluid swirling chamber defined bythe cylindrical member and the first and second end wall members, onefluid inlet hole extending through the wall of the cylindrical member ata position closer to the second end wall member than the center in theaxial direction of the cylindrical member to introduce a gas-liquidmixed fluid into the fluid swirling chamber in a tangential directionthereof, and a fluid outlet hole extending through the second end wallmember along the center axis of the inner peripheral surface of thecylindrical member.

The feature of this fine bubble generating apparatus resides in that thefluid inlet hole is provided at a position closer to the second end wallmember than the center in the axial direction of the cylindrical member.With this arrangement, unlike in the aforementioned fine bubblegenerating apparatus having one fluid inlet hole, most of the gas-liquidmixed fluid introduced into the fluid swirling chamber through the fluidinlet hole moves in a swirling flow toward the first end wall member,which has no outlet hole, and is reversed by the first end wall memberwhile being directed toward the radial center of the fluid swirlingchamber. Thereafter, while further increasing the swirling velocity, thefluid moves toward the second end wall member and is discharged to theoutside through the fluid outlet hole.

That is, in the foregoing conventional apparatus, the gas-liquid mixedfluid introduced into the fluid swirling chamber simply moves toward theoutlet hole. In this fine bubble generating apparatus, unlike in theconventional apparatus, most of the gas-liquid mixed fluid introducedinto the fluid swirling chamber once moves in a swirling flow in adirection away from the outlet hole. The swirling flow is reversed bythe first end wall member to move therefrom toward the second end wallmember. At this time, the radius of rotation of the swirling flow movingtoward the second end wall member is smaller than that of the swirlingflow moving toward the first end wall member. Therefore, the flowvelocity increases, and the shear force acting on the gas contained inthe liquid increases. Thus, breaking up of the gas is accelerated.

Specifically, the fluid inlet hole may be configured to be close to thesecond end wall member. More specifically, the fluid inlet hole may havea circular sectional shape and may be positioned away from the secondend wall member in the axial direction by a distance at least 0.5 to 2times the diameter of the fluid inlet hole.

The reason why the fluid inlet hole is not positioned in contact withthe second end wall member is to prevent the swirling velocity of thegas-liquid mixed fluid introduced through the fluid inlet hole frombeing reduced by frictional resistance that would otherwise be offeredby the second end wall member.

Preferably, the fluid swirling chamber has an axial length not less than6 times the diameter of the fluid inlet hole. The reason for this is tolengthen, as much as possible, the path of swirling flow moving towardthe first end wall member and the path of swirling flow moving from thefirst end wall member toward the second end wall member.

Further, it is preferable that the fluid inlet hole be configured toextend at an angle of from 10° to 30°, more preferably about from 15° to20°, to a direction in which the fluid inlet hole would extend if it isassumed to internally touch the inner wall surface of the fluid swirlingchamber and extend tangentially, about the point of internal tangency tothe inner wall surface of the fluid swirling chamber. The numericalvalues of the angle were obtained from a gas swirling shearing unitactually made on an experimental basis. It was possible with this gasswirling shearing unit to generate nanobubbles more efficiently than inthe case of setting the fluid inlet hole to extend in the truetangential direction.

The inner peripheral surface of the cylindrical member may bemirror-finished, and a portion of the inner peripheral surface of thecylindrical member that circumferentially corresponds to the fluid inlethole, which opens on the inner peripheral surface, may be provided witha plurality of annular grooves spaced from each other in the axialdirection of the inner peripheral surface. The annular grooves have awidth and a depth that are not more than 1 millimeter.

With the above-described structure, it is possible to form thegas-liquid mixed fluid introduced into the fluid swirling chamber into aswirling flow while keeping it from expanding much in the axialdirection.

The cylindrical member and the first and second end wall members have anatural frequency different from a frequency generated by the fluidintroduced into the fluid swirling chamber through the fluid inlet hole.The reason for this is to prevent the vibration of the cylindricalmember from increasing, which would otherwise hinder smooth generationof swirling flow.

More specifically, the fine bubble generating apparatus may furtherinclude a vortex pump connected to the fluid inlet hole of the gasswirling shearing unit to supply a fluid to the fluid swirling chamber.The vortex pump has a casing, an impeller rotating in the casing, aliquid inlet formed in the peripheral wall of the casing, a gas inletformed in the peripheral wall of the casing, and a fluid outlet providedin the peripheral wall of the casing to deliver a gas-liquid mixed fluidformed from a liquid and gas sucked into the casing and mixed togetherby rotation of the impeller. The fluid outlet of the vortex pump isconnected to the fluid inlet hole of the gas swirling shearing unit. Theuse of such a vortex pump enables the gas to be broken up into finebubbles before being introduced into the gas swirling shearing unit andhence allows nanobubbles to be generated even more efficiently.

Preferably, a disperser is connected to the fluid outlet hole of the gasswirling shearing unit to dispersedly discharge the fluid delivered fromthe gas swirling shearing unit. Specifically, the disperser may have acylindrical member having a cylindrical inner peripheral surface, endwall members configured to close both ends of the cylindrical member, afluid inlet formed in an axially central portion of the cylindricalmember in communication with the fluid outlet hole of the gas swirlingshearing unit, and fluid outlets extending through the end wall members,respectively, along the axis of the cylindrical member.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a fine bubble generating apparatusaccording to the present invention.

FIG. 2 is a diagram for explaining the interior of a gas swirlingshearing unit used in the fine bubble generating apparatus.

FIG. 3 is a sectional view taken along the line III-III in FIG. 2.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the fine bubble generating apparatus according to thepresent invention will be explained below with reference to theaccompanying drawings.

FIG. 1 is an explanatory view of a fine bubble generating apparatus 10according to the present invention. The apparatus 10 has a vortex pump12, a gas swirling shearing unit 14, and a disperser 16. The pump 12forms a gas-liquid mixed fluid. The gas swirling shearing unit 14receives the gas-liquid mixed fluid formed in the vortex pump 12 andbreaks up a gas contained in the gas-liquid mixed fluid into finebubbles. The disperser 16 dispersedly discharges the fluid in which thegas has been broken up into fine bubbles by the gas swirling shearingunit 14. The disperser 16 is immersed in a liquid L in a liquid storagetank 36 to dispersedly discharge fine bubbles into the liquid L in theliquid storage tank 36. The liquid L in the liquid storage tank 36 issupplied to the pump 12 through a pipe 38.

The vortex pump 12 has a housing 20 and an impeller 22 housed in thehousing 20 and driven to rotate. The housing 20 is provided with aliquid suction hole 24, a gas suction hole 26 and a delivery hole 28.The liquid suction hole 24 is connected with the pipe 38 to suck theliquid in the liquid storage tank 36 into the pipe 38. The gas suctionhole 26 is communicated with the liquid suction hole 24 so that a gas issucked into the liquid flowing through the liquid suction hole 24. Thedelivery hole 28 delivers a gas-liquid mixed fluid formed from theliquid and gas sucked into the housing 20 and mixed together by rotationof the impeller 22. The delivery hole 28 has a smaller diameter thanthat of the liquid suction hole 24 to increase the speed of the fluiddelivered to the gas swirling shearing unit 14.

The gas suction hole 26 is connected with a pipe 30 that is providedwith a solenoid valve 32. The solenoid valve 32 is closed when the pump12 is started. The solenoid valve 32 is opened when a predetermined time(e.g. 60 seconds) has elapsed after the start of the pump 12. This isdone to minimize the occurrence of cavitation in the pump 12 due tosuction of gas into the pump 12.

The gas swirling shearing unit 14 has, as shown in FIGS. 2 and 3, acylindrical member 40 having a cylindrical inner peripheral surface, afirst end wall member 42 configured to close one end of the cylindricalmember 40, a second end wall member 44 configured to close the other endof the cylindrical member 40, a fluid swirling chamber 46 defined by thecylindrical member 40 and the first and second end wall members 42 and44, a fluid inlet hole 48 extending through the wall of the cylindricalmember 40 at a position closer to the second end wall member 44 than thecenter in the axial direction of the cylindrical member 40 to introducethe gas-liquid mixed fluid into the fluid swirling chamber 46 in atangential direction thereof, and a fluid outlet hole 50 extendingthrough the second end wall member 44 along the center axis of the innerperipheral surface of the cylindrical member 40.

In the illustrated example, a connecting pipe 54 is secured to the outerperipheral surface of the cylindrical member 40 in communication withthe fluid inlet hole 48. The pipe 54 is connected to a pipe 55 extendingfrom the delivery hole 28 of the pump 12. A connecting pipe 52[54] issecured to the second end wall member 44 in communication with the fluidoutlet hole 50. The pipe 52[54] is connected to a pipe extending to thedisperser 16.

In the illustrated example, the fluid inlet hole 48 is configured to beclose to the second end wall member 44. Specifically, the fluid inlethole 48 has a circular sectional shape and is positioned away from thesecond end wall member 44 by a distance substantially equal to thediameter of the fluid inlet hole 48.

The fluid swirling chamber 46 has an axial length not less than 5 timesthe diameter of the fluid inlet hole 48 and a diameter not less than 4times the diameter of the fluid inlet hole 48. In the illustratedexample, the axial length of the fluid swirling chamber 46 is about 12times the diameter of the fluid inlet hole 48, and the diameter of theformer is about 5 times the diameter of the latter.

The fluid inlet hole 48 and the connecting pipe 54 communicatedtherewith has an axis intersecting with a hypothetical axis T of thefluid inlet hole 48, that is assumed to intersect with an inner wallsurface of the fluid swirling chamber 46 and extend tangentially, at apoint I where the hypothetical axis touches the inner wall surface at anangle of from 10 to 30 degrees, preferably about from 15° to 20°.

The inner peripheral surface of the cylindrical member 40 ismirror-finished, and a portion of the inner peripheral surface thatcircumferentially corresponds to the fluid inlet hole 48, which opens onthe inner peripheral surface, is provided with a plurality of annulargrooves 56 spaced from each other in the axial direction of the innerperipheral surface. The annular grooves 56 have a width and a depth thatare not more than 1 millimeter. In the illustrated example, an innerperipheral surface portion that circumferentially corresponds to thefluid inlet hole 48 is provided with five grooves, and one additionalgroove is provided at each side of the inner peripheral surface portionprovided with the five grooves. Specific dimensions of the annulargrooves 56 are 0.3 mm in depth and 0.5 mm in width.

The cylindrical member 40 and the first and second end wall members 42and 44 are designed to have mass and so forth that have a naturalfrequency different from a frequency generated by the fluid introducedinto the fluid swirling chamber 46 through the fluid inlet hole 48.

The disperser 16 has a cylindrical member 60 with a cylindrical innerperipheral surface and end wall members 62 configured to close both endsof the cylindrical member 60. The disperser 16 further has a fluid inlet64 formed in an axially central portion of the cylindrical member 60 incommunication with the fluid outlet hole 50 of the gas swirling shearingunit 14. Further, the disperser 16 has fluid outlets 66 extendingthrough the end wall members 62, respectively, along the axis of thecylindrical member 60.

The fluid delivered from the fluid outlet hole 50 of the gas swirlingshearing unit 14 flows into the disperser 16 through the fluid inlet 64of the disperser 16, separates into two streams flowing toward theaxially opposite ends of the disperser 16 while swirling and isdispersedly discharged into the liquid in the liquid storage tank 36from the fluid outlets 66.

To operate the fine bubble generating apparatus 10, the pump 12 isdriven to suck in the liquid from the liquid storage tank 36, therebyinducing a flow of liquid circulating from the pump 12 through the gasswirling shearing unit 14 and the disperser 16 to the liquid storagetank 36.

The solenoid valve 32 is opened when a predetermined time, e.g. 60seconds, has elapsed after the start of the pump 12. Consequently, airis sucked in through the pipe 30, and thus a gas-liquid mixed fluid isintroduced into the housing 20 of the pump 12. The gas-liquid mixedfluid introduced into the pump housing 20 is driven to move along theinner peripheral surface of the housing 20 by the action of the impeller22 and delivered through the delivery hole 28. Meanwhile, the gas in thefluid is broken up into fine bubbles by shear force from turbulent flowoccurring in the fluid. Some bubbles obtained at this stage may have adiameter of micrometer level.

The gas-liquid mixed fluid from the delivery hole 28 is introduced intothe fluid swirling chamber 46 of the gas swirling shearing unit 14,where the fluid is formed into a swirling flow as stated above. Thus,the gas in the fluid is further broken up into fine bubbles by thestrong shear force of the swirling flow. The strong shear force in thegas swirling shearing unit 14 enables most bubbles to break up into finebubbles on the nanometer level.

The gas-liquid mixed fluid delivered from the gas swirling shearing unit14 is discharged into the liquid storage tank 36 while being formed intoa swirling flow again by the disperser 16. Accordingly, breaking up ofbubbles also takes place in the disperser 16.

In the illustrated example, the liquid is circulated from the liquidstorage tank 36 through the pump 12, the gas swirling shearing unit 14and the disperser 16. In this regard, the supply of the liquid to thepump 12 may be performed from other than the liquid storage tank 36.However, if the liquid is circulated as in the illustrated example,breaking up of the gas is performed repeatedly, and it is thereforepossible to obtain even finer bubbles.

As a specific example, the cylindrical member 40 and the end wallmembers 42 and 44 of the gas swirling shearing unit 14 were formed fromstainless steel having a thickness of 10 mm. The fluid swirling chamber46 was formed with an axial length of 110 mm and an inner diameter of 43mm to 55 mm. The fluid inlet hole 48 and the connecting pipe 54 each hadan inner diameter of 10 mm. The distance from the second end wall member44 to the center line of the fluid inlet hole 48 was 20 mm. The mountingangle θ of the connecting pipe 54 was about 18 degrees. The deliveryfrom the pump 12 was 120 liters per minute. In this case, generation ofa large number of fine bubbles on the nanometer level was confirmed.

In the foregoing, one embodiment of the fine bubble generating apparatusaccording to the present invention has been described. It should benoted that the fine bubble generating apparatus is usable in variousapplications as follows.

For example, water containing nanobubbles (hereinafter referred to as“nanobubble water”) generated by the fine bubble generating apparatusaccording to the present invention is superior in surface activity andwettability and usable for fibers, metallic molds, machine parts,silicon wafers and various other purposes. For washing silicon wafers,nanobubble water containing nitrogen bubbles should preferably be used.To mine extra-heavy oil out from underground, it is general practice toinject water containing a surface-active agent into an extra-heavy oildeposit located deep under the ground and to suck up extra-heavy oilmixed with the water. In this regard, if nanobubble water is used, it ispossible to reduce the amount of surface-active agent used. It is alsopossible to reduce to a considerable extent the work needed to separatethe obtained extra-heavy oil from the surface-active agent.

In addition, nanobubble water has a high penetrability and is thereforeusable in alcohol brewing, for example. That is, to brew rice wine(sake), for example, polished rice is dipped in water for about 24 hoursbefore being steamed. In this case, if rice is dipped in nanobubblewater, the dipping time can be reduced to about 6 hours, i.e. one fourthof the conventional dipping time.

In making bread or fish paste products, if wheat flour or fish iskneaded with nanobubble water prepared by using nitrogen, aerobicbacteria in the wheat flour or fish die. Therefore, it becomes possibleto prevent decomposition of the bread or fish paste products withoutusing a preservative.

Nanobubble water can also be used to purify river water, etc. Ifnanobubble water is used in a wastewater treatment system employing theactivated sludge process, in particular, activated sludge, i.e.bacteria, can be activated, and the purification efficiency can beincreased.

Further, if oxygen or air nanobubbles are generated in petroleum orother combustion oil by the fine bubble generating apparatus accordingto the present invention, the combustion efficiency of the oil can beimproved to a considerable extent.

Further, nanobubbles offer physiological activity. For example, if handsare immersed in nanobubble water, the pores of the hands open, and sebumin the pores can be removed. If nanobubble water is used for a hot bath,the hot bath effect can be enhanced.

If nanobubbles in nanobubble water are destroyed by ultrasonic waves orlight energy, explosive power can be generated in microscopic areas.Through this technique, nanobubble water can be used to cut genes ingenetic recombination, for example.

1. A fine bubble generating apparatus comprising a gas swirling shearingunit, the gas swirling shearing unit including: a cylindrical memberhaving a cylindrical inner peripheral surface; a first end wall memberconfigured to close one end of the cylindrical member; a second end wallmember configured to close the other end of the cylindrical member; afluid swirling chamber defined by the cylindrical member, the first endwall member and the second end wall member; a fluid inlet hole extendingthrough a wall of the cylindrical member at a position closer to thesecond end wall member than a center in an axial direction of thecylindrical member to introduce a gas-liquid mixed fluid into the fluidswirling chamber in a tangential direction thereof; and a fluid outlethole extending through the second end wall member along a center axis ofthe inner peripheral surface of the cylindrical member.
 2. The finebubble generating apparatus of claim 1, wherein the fluid inlet hole isset close to the second end wall member.
 3. The fine bubble generatingapparatus of claim 2, wherein the fluid inlet hole has a circularsectional shape and is positioned away from the second end wall memberin the axial direction by a distance at least 0.5 to 2 times a diameterof the fluid inlet hole.
 4. The fine bubble generating apparatus ofclaim 3, wherein the fluid swirling chamber has an axial length not lessthan 6 times the diameter of the fluid inlet hole.
 5. The fine bubblegenerating apparatus of claim 1, wherein the fluid inlet hole has anaxis intersecting with a hypothetical axis of the fluid inlet hole, thatis assumed to intersect with an inner wall surface of the fluid swirlingchamber and extend tangentially, at a point where the hypothetical axistouches the inner wall surface at an angle of from 10 to 30 degrees. 6.The fine bubble generating apparatus of claim 5, wherein the innerperipheral surface of the cylindrical member is mirror-finished, and aportion of the inner peripheral surface of the cylindrical member thatcircumferentially corresponds to the fluid inlet hole, which opens onthe inner peripheral surface, is provided with a plurality of annulargrooves spaced from each other in an axial direction of the innerperipheral surface, the annular grooves having a width and a depth thatare not more than 1 millimeter.
 7. The fine bubble generating apparatusof claim 5, wherein the cylindrical member and the first end wall memberand second end wall member have a natural frequency different from afrequency generated by the fluid introduced into the fluid swirlingchamber through the fluid inlet hole.
 8. The fine bubble generatingapparatus of claim 1, further comprising a vortex pump connected to thefluid inlet hole of the gas swirling shearing unit to supply a fluid tothe fluid swirling chamber, the vortex pump including: a casing; animpeller rotating in the casing; a liquid inlet formed in a peripheralwall of the casing; a gas inlet formed in the peripheral wall of thecasing; and a fluid outlet provided in the peripheral wall of the casingto deliver a gas-liquid mixed fluid formed from a liquid and gas suckedinto the casing and mixed together by rotation of the impeller, thefluid outlet being connected to the fluid inlet hole of the gas swirlingshearing unit.
 9. The fine bubble generating apparatus of claim 8,further comprising a disperser connected to the fluid outlet hole of thegas swirling shearing unit to dispersedly discharge the fluid deliveredfrom the gas swirling shearing unit.
 10. The fine bubble generatingapparatus of claim 9, wherein the disperser includes: a cylindricalmember having a cylindrical inner peripheral surface; end wall membersconfigured to close both ends of the cylindrical member; a fluid inletformed in an axially central portion of the cylindrical member incommunication with the fluid outlet hole of the gas swirling shearingunit; and fluid outlets extending through the end wall members,respectively, along an axis of the cylindrical member.
 11. A washingmethod comprising the steps of: preparing water containing fine bubblesby using the fine bubble generating apparatus of claim 1; and washing anarticle with the water.
 12. A method of increasing a water content ofgrains, the method comprising the steps of: preparing water containingfine bubbles by using the fine bubble generating apparatus of claim 1;and dipping the grains in the water.
 13. A kneaded food materialproducing method comprising the steps of: preparing water containingfine nitrogen bubbles by using the fine bubble generating apparatus ofclaim 1; and producing a kneaded food material by using the water.
 14. Amethod of producing a combustion oil of improved combustion efficiency,the method comprising the steps of: providing the fine bubble generatingapparatus of claim 1; and generating fine oxygen bubbles in thecombustion oil by using the fine bubble generating apparatus.
 15. Amethod of activating activated sludge in an activated sludge wastewatertreatment system, the method comprising the steps of: providing the finebubble generating apparatus of claim 1; and generating fine bubbles inwater in the wastewater treatment system by using the fine bubblegenerating apparatus, thereby activating the activated sludge.
 16. Anextra-heavy oil mining method comprising the steps of: supplying anextra-heavy oil deposit with water containing fine bubbles prepared byusing the fine bubble generating apparatus of claim 1; and sucking upthe water together with extra-heavy oil.
 17. A method of enhancing hotbath effect, the method comprising the steps of: preparing watercontaining fine bubbles by using the fine bubble generating apparatus ofclaim 1; and using the water for a hot bath.